The Experts below are selected from a list of 216 Experts worldwide ranked by ideXlab platform

Jennifer E. Smith - One of the best experts on this subject based on the ideXlab platform.

  • Gradients in Primary Production Predict Trophic Strategies of Mixotrophic Corals across Spatial Scales
    Current biology : CB, 2018
    Co-Authors: Michael D. Fox, Gareth J. Williams, Maggie D. Johnson, Veronica Z. Radice, Brian J. Zgliczynski, Emily L. A. Kelly, Forest Rohwer, Stuart A. Sandin, Jennifer E. Smith
    Abstract:

    Summary Mixotrophy is among the most successful Nutritional strategies in terrestrial and marine ecosystems. The ability of organisms to supplement primary Nutritional modes along continua of autotrophy and heterotrophy fosters trophic flexibility that can sustain metabolic demands under variable or stressful conditions. Symbiotic, reef-building corals are among the most broadly distributed and ecologically important mixotrophs, yet we lack a basic understanding of how they modify their use of autotrophy and heterotrophy across gradients of food availability. Here, we evaluate how one coral species, Pocillopora meandrina, supplements autotrophic Nutrition through heterotrophy within an archipelago and test whether this pattern holds across species globally. Using stable isotope analysis (δ13C) and satellite-derived estimates of nearshore primary production (chlorophyll-a, as a proxy for food availability), we show that P. meandrina incorporates a greater proportion of carbon via heterotrophy when more food is available across five central Pacific islands. We then show that this pattern is consistent globally using data from 15 coral species across 16 locations spanning the Caribbean Sea and the Indian and Pacific Oceans. Globally, surface chlorophyll-a explains 77% of the variation in coral Heterotrophic Nutrition, 86% for one genus across 10 islands, and 94% when controlling for coral taxonomy within archipelagos. These results demonstrate, for the first time, that satellite-derived estimates of nearshore primary production provide a globally relevant proxy for resource availability that can explain variation in coral trophic ecology. Thus, our model provides a pivotal step toward resolving the biophysical couplings between mixotrophic organisms and spatial patterns of resource availability in the coastal oceans.

David A Caron - One of the best experts on this subject based on the ideXlab platform.

  • Gene expression characterizes different Nutritional strategies among three mixotrophic protists.
    FEMS microbiology ecology, 2016
    Co-Authors: Zhenfeng Liu, Victoria Campbell, Karla B. Heidelberg, David A Caron
    Abstract:

    Mixotrophic protists, i.e. protists that can carry out both phototrophy and heterotrophy, are a group of organisms with a wide range of Nutritional strategies. The ecological and biogeochemical importance of these species has recently been recognized. In this study, we investigated and compared the gene expression of three mixotrophic protists, Prymnesium parvum , Dinobyron sp. and Ochromonas sp. under light and dark conditions in the presence of prey using RNA-Seq. Gene expression of the obligately phototrophic P. parvum and Dinobryon sp. changed significantly between light and dark treatments, while that of primarily Heterotrophic Ochromonas sp. was largely unchanged. Gene expression of P. parvum and Dinobryon sp. shared many similarities, especially in the expression patterns of genes related to reproduction. However, key genes involved in central carbon metabolism and phagotrophy had different expression patterns between these two species, suggesting differences in prey consumption and Heterotrophic Nutrition in the dark . Transcriptomic data also offered clues to other physiological traits of these organisms such as preference of nitrogen sources and photo-oxidative stress. These results provide potential target genes for further exploration of the mechanisms of mixotrophic physiology and demonstrate the potential usefulness of molecular approaches in characterizing the Nutritional modes of mixotrophic protists.

  • Mixotrophy stirs up our understanding of marine food webs.
    Proceedings of the National Academy of Sciences of the United States of America, 2016
    Co-Authors: David A Caron
    Abstract:

    Mixotrophy among planktonic eukaryotic organisms is broadly defined as the combined use of photosynthetic and Heterotrophic Nutrition within a single organism. The conventional view of species as either phototrophic (capable of producing energy and carbon for growth using only inorganic compounds and light) or Heterotrophic (wholly dependent on preformed organic material for Nutrition) is a preconception rooted in the fact that most terrestrial species can easily be divided into “plants” or “animals.” Indeed, the diversity of terrestrial organisms that combine photosynthetic and Heterotrophic Nutrition is mostly relegated to a dozen or so genera of carnivorous plants that capture and digest insects and other small creatures for the nutrients they contain, but also capture light energy via photosynthesis. In contrast to life on land, mixotrophic Nutrition is widespread among single-celled and multicellular organisms comprising the ocean’s plankton. The ecological significance for the species that possess this behavior has not been lost on biologists who have endeavored to document and understand mixotrophy, but its importance to pelagic food-web structure and function has not yet become entrained into mathematical models of marine ecosystems. In PNAS, Ward and Follows (1) address this disparity, and provide one of the first attempts to incorporate mixotrophic Nutrition into biogeochemical models of oceanic food webs. The authors use their model to estimate the impact that mixotrophy has on food-web structure, the efficiency of carbon transfer to higher trophic levels, and the sinking of carbon into the deep ocean.

  • EFFECTS OF LIGHT AND GLYCEROL ON THE ORGANIZATION OF THE PHOTOSYNTHETIC APPARATUS IN THE FACULTATIVE HETEROTROPH PYRENOMONAS SALINA (CRYPTOPHYCEAE)1
    Journal of Phycology, 1991
    Co-Authors: Alan J. Lewitus, David A Caron, Kenneth R. Miller
    Abstract:

    The marine cryptophyte Pyrenomonas salina Santore is capable of autotrophic and Heterotrophic Nutrition. We studied the physiological and ultrastructural changes that accompany the shift between these Nutritional modes. The addition of glycerol to batch cultures of P. salina, grown at an irradiance limiting for photoautotrophic growth, increased its growth rate and induced specific biochemical and structural changes in its photosynthetic system. Results from extracted pigment analyses, thin-section electron microscopy, and freeze-fracture electron microscopy indicated that glycerol addition reduced the cell phycoerythrin content, phycoerythrin to chlorophyll a ratio, degree of thylakoid packing, number of thylakoids · cell−1, and PSII particle size. These properties were reduced to a similar extent in cells grown photoautotrophically under an irradiance saturating for growth. These results are consistent with the hypothesis that enhancement of Heterotrophic potential occurs at the expense of light-harvesting ability in glycerol-grown P. salina.

Ruth D. Gates - One of the best experts on this subject based on the ideXlab platform.

  • Spatial variation in the biochemical and isotopic composition of corals during bleaching and recovery
    Limnology and oceanography, 2019
    Co-Authors: Christopher B. Wall, Raphael Ritson-williams, Brian N. Popp, Ruth D. Gates
    Abstract:

    Ocean warming and the increased prevalence of coral bleaching events threaten coral reefs. However, the biology of corals during and following bleaching events under field conditions is poorly understood. We examined bleaching and postbleaching recovery in Montipora capitata and Porites compressa corals that either bleached or did not bleach during a 2014 bleaching event at three reef locations in Kāne'ohe Bay, O'ahu, Hawai'i. We measured changes in chlorophylls, tissue biomass, and Nutritional plasticity using stable isotopes (δ13C, δ15N). Coral traits showed significant variation among periods, sites, bleaching conditions, and their interactions. Bleached colonies of both species had lower chlorophyll and total biomass, and while M. capitata chlorophyll and biomass recovered 3 months later, P. compressa chlorophyll recovery was location dependent and total biomass of previously bleached colonies remained low. Biomass energy reserves were not affected by bleaching, instead M. capitata proteins and P. compressa biomass energy and lipids declined over time and P. compressa lipids were site specific during bleaching recovery. Stable isotope analyses did not indicate increased Heterotrophic Nutrition in bleached colonies of either species, during or after thermal stress. Instead, mass balance calculations revealed that variations in δ13C values reflect biomass compositional change (i.e., protein : lipid : carbohydrate ratios). Observed δ15N values reflected spatiotemporal variability in nitrogen sources in both species and bleaching effects on symbiont nitrogen demand in P. compressa. These results highlight the dynamic responses of corals to natural bleaching and recovery and identify the need to consider the influence of biomass composition in the interpretation of isotopic values in corals.

  • Spatial variation in the biochemical and isotopic composition of corals during bleaching and recovery
    2018
    Co-Authors: Christopher B. Wall, Raphael Ritson-williams, Brian N. Popp, Ruth D. Gates
    Abstract:

    Ocean warming and the increased prevalence of coral bleaching events threaten coral reefs. However, the biology of corals during and following bleaching events under field conditions is poorly understood. We examined bleaching and post-bleaching recovery in Montipora capitata and Porites compressa corals that either bleached or did not bleach during a 2014 bleaching event at three reef locations in Kāne9ohe Bay, O9ahu. We measured changes in chlorophylls, biomass, and Nutritional plasticity using stable isotopes (δ 13 C, δ 15 N). Coral traits showed significant variation among bleaching conditions, reef sites, time periods, and their interactions. Bleached colonies of both species had lower chlorophyll and total biomass. While M. capitata chlorophyll and biomass recovered three months later, P. compressa chlorophyll recovery was location-dependent and total biomass of previously bleached colonies remained low. Biomass energy reserves were not affected by bleaching, instead M. capitata proteins and P. compressa biomass energy declined over time, and P. compressa lipid biomass was site-specific. Stable isotope analyses of host and symbiont tissues did not indicate increased Heterotrophic Nutrition in bleached colonies of either species, during or after thermal stress. Instead, mass balance calculations revealed variance in δ 13 C values was best explained by augmented biomass composition, whereas δ 15 N values reflected spatial and temporal variability in nitrogen sources in addition to bleaching effects on symbiont nitrogen demand. These results emphasize total biomass quantity may change substantially during bleaching and recovery. Consequently, there is a need to consider the influence of biomass composition in the interpretation of isotopic values in corals.

Christine Ferrier-pages - One of the best experts on this subject based on the ideXlab platform.

  • Trophic dynamics of scleractinian corals: stable isotope evidence
    Journal of Experimental Biology, 2015
    Co-Authors: Pascale Tremblay, Jean-françois Maguer, Renaud Grover, Christine Ferrier-pages
    Abstract:

    Reef-building corals form symbioses with dinoflagellates from the diverse genus Symbiodinium. This symbiotic association has developed adaptations to acquire and share nutrients, which are essential for its survival and growth in nutrient-poor tropical waters. The host is thus able to prey on a wide range of organic food sources (Heterotrophic Nutrition) whereas the symbionts acquire most of the inorganic nutrients (autotrophic Nutrition). However, nutrient fluxes between the two partners remain unclear, especially concerning Heterotrophically acquired carbon and nitrogen. We combined physiological measurements and pulse-chase isotopic labeling of Heterotrophic carbon and nitrogen, as well as autotrophic carbon to track nutrient fluxes in two coral species, Stylophora pistillata and Turbinaria reniformis, in symbiosis with Symbiodinium clades A, and C, D respectively. We showed a rapid acquisition, exchange and a long-term retention of Heterotrophic nutrients within the symbiosis, whereas autotrophic nutrients were rapidly used to meet immediate metabolic needs. In addition, there was a higher retention of Heterotrophic nitrogen compared with carbon, in agreement with the idea that tropical corals are nitrogen-limited. Finally, a coupling between auto-and heterotrophy was observed in the species S. pistillata, with a higher acquisition and retention of Heterotrophic nutrients under low irradiance to compensate for a 50% reduction in autotrophic nutrient acquisition and translocation. Conversely, T. reniformis conserved an equivalent Heterotrophic nutrient acquisition at both light levels because this coral species did not significantly reduce its rates of gross photosynthesis and autotrophic carbon acquisition between the two irradiances. These experiments advance the current understanding of the nutrient exchanges between the two partners of a symbiotic association, providing evidence of the complexity of the host-symbiont relationship.

  • Microheterotrophy in the zooxanthellate coral Stylophora pistillata: Effects of light and ciliate density
    Limnology and Oceanography, 1998
    Co-Authors: Christine Ferrier-pages, Denis Allemand, Jean-pierre Gattuso, Jean Jaubert, Fereidoun Rassoulzadegan
    Abstract:

    We examined the ability of the zooxanthellate coral Stylophora pistillata (Esper, 1797) to feed on microheterotrophs (bacteria and oligotrichous ciliates). The effect of light on the feeding rates was also investigated. Grazing experiments were first conducted by exposing coral colonies to known amounts of 3 H-thymidine-labeled bacteria and ciliates and measuring the appearance of radioactivity in coral tissues. A method was developed to obtain clean cultures of 3 H-labeled ciliates. Results showed that 7% of the labeled bacteria and 90% of the labeled ciliates were ingested after 4-6 h incubation. Corals were then incubated in medium containing different concentrations of unlabeled ciliates (200, 500, 800 cells ml -1 ). Replicates of each concentration were exposed to one of three light levels (0, 80, 250 μmol m -2 s -1 ). Coral feeding rate increased with prey density, from 1.40 to 4.10 × 104 ciliates (0.22-0.65 μg C mg protein-' h-') for 200-800 ciliates ml-', respectively. However, a plateau was observed after a total ingestion of 4 × 10 4 ciliates (1.7 μgC mg protein '). The total number of ciliates ingested, as well as the ingestion rates decreased when the light intensity increased. During dark experiments, the maximal amount of carbon ingested was twice as much as that ingested in light experiments. However, Heterotrophic Nutrition occurred even if the colonies could satisfy their carbon metabolism via photosynthesis. Zooplankton feeding seems therefore to complement autotrophic Nutrition. Under high light, the small amount of microplankton ingested may provide nitrogen, phosphorus, or vitamins to corals, and this food supply may be especially important in tropical waters where inorganic nutrient concentrations are low. Conversely, when light is limiting, predation may also provide most of the energy necessary for coral maintenance.

Herwig Stibor - One of the best experts on this subject based on the ideXlab platform.

  • delta C-13, delta N-15, and C:N ratios as Nutrition indicators of zooxanthellate jellyfishes: insights from an experimental approach
    Journal of Experimental Marine Biology and Ecology, 2020
    Co-Authors: Nicolas Djeghri, Herwig Stibor, Oanez Lebeau, Philippe Pondaven
    Abstract:

    Some jellyfish host zooxanthellae in their tissues (mostly from the family Symbiodiniaceae; Dinophyceae) and supplement their Heterotrophic Nutrition with their symbiont's photosynthates. The mixotrophy of zooxanthellate jellyfishes (as holobionts) renders the study of their Nutrition, growth, and population dynamics complicated. Here, we used an experimental approach to assess how carbon and nitrogen stable isotopes (delta C-13 and delta N-15) as well as the elemental composition (C:N ratios) of zooxanthellate jellyfishes are affected by variations in Nutrition sources: i.e. predation (Heterotrophic) versus photosynthesis (autotrophic). Our laboratory experiment, conducted on the zooxanthellate jellyfish Cassiopea sp. medusae (including symbionts) in the presence or absence of light and prey during 24 days, showed conclusive results. Presence of light decreased delta N-15, increased delta C-13 and C:N ratios, whereas presence of prey increased delta N-15, and decreased delta C-13 and C:N ratios. The medusae incubated with both light and prey had intermediate delta N-15, delta C-13 and C:N ratios. Variations in zooxanthellate jellyfishes' Nutrition sources (autotrophy vs. heterotrophy) are thus reflected by their isotopic and elemental composition. By disentangling the effects of autotrophy and of heterotrophy on zooxanthellate jellyfish isotopic and elemental compositions, these results would help to interpret the values of delta C-13, delta N-15 and C:N ratios that can be observed on these organisms in fieldwork studies.

  • Mixotrophic versus photoautotrophic specialist algae as food for zooplankton: The light : nutrient hypothesis might not hold for mixotrophs
    Limnology and Oceanography, 2005
    Co-Authors: Alexis Katechakis, Tanja Haseneder, Robert Kling, Herwig Stibor
    Abstract:

    We reared mixotrophic (Ochromonas tuberculata and Cryptomonas sp.) and photoautotrophic specialist algae (Scenedesmus obliquus) at different light : phosphorus supplies and compared their effects as food for zooplankton (Daphnia magna). According to the light : nutrient hypothesis (LNH), biomass and nutrient stoichiometry of phototrophic specialists depend strongly on light : phosphorus supplies. If this is true, herbivore growth and fecundity should be limited by food quantity at low light intensities and by stoichiometric food quality at high light intensities. In turn, phosphorus fertilization should cause a transition from limitation by food quality to limitation by food quantity. In contrast to the LNH, biomass and nutrient stoichiometry of mixotrophs were almost unaffected by alterations in the supply of light and dissolved nutrients. Bacterial counts indicate that mixotrophs compensated for light or phosphorus deficiency by Heterotrophic Nutrition. Compared to phototrophic specialists, a diet of Cryptomonas sp. therefore enabled a similar or higher and more stable secondary production at most light : nutrient supplies. O. tuberculata, however, appeared to be toxic. Our results indicate that mixotrophs might have a balancing effect on variations in transfer efficiency caused by perturbations to light and nutrient supplies.

  • Mixotrophy of a photosynthetic flagellate viewed from an optimal foraging perspective.
    Protist, 2003
    Co-Authors: Herwig Stibor, Ulrich Sommer
    Abstract:

    Mixotrophy, a combination of phototrophic and phagotrophic Nutrition, has been found in several classes of phytoplankton (Booras et al. 1988, Jones 2000) and appears to be a successful evolutionary strategy. Heterotrophic Nutrition of phytoplankton has been suggested to be an important source of mineral nutrients (Nygaard and Tobiesen 1993). Potentially limiting mineral nutrients, particularly phosphorus (P), are often several orders of magnitude more concentrated in the biomass of food organisms of mixotrophs (e.g. in bacteria) than in the dissolved phase (Vadstein 2000). We used radioactive tracer experiments to show that the simultaneous uptake of P from dissolved inorganic and particular P sources by the marine phytoflagellate Chrysochromulina polylepis followed basic predictions of optimal foraging theory (Stephens and Krebs 1986). Chrysochromulina takes up its P rather unselectively from both bacterial P and dissolved P sources at low dissolved P concentrations, while it becomes more selective at higher dissolved inorganic P (DIP) concentrations. The onset of mixotrophic processes was dependent on DIP concentrations. These findings support the view of mixotrophy as a strategy of nutrient uptake in nutrient poor (oligotrophic) pelagic environments (Nygaard and Tobiesen 1993) and show that ideas of optimal foraging can be applied to unicellular organisms.